FUEL. 171 allowed to escape directly into the stack, but it is much more economical to let it pass through a boiler. The amount of heat available varies with the condition of the charge, being less after the furnace is filled with cold blooms and greatest when they are at the full heat. The boiler need not be big enough to absorb all the waste heat during the short period when the furnace is hottest, but should be more than big enough to handle the minimum. Steam must be made, and if not made by this waste heat then it must be supplied from the fire-room. Following is a general statement of the heat balance: (1) For each ton of coal used in twelve hours in the firebox, the waste heat from the furnace averages from 25 to 30 horsepower. (2) A furnace at its highest heat represents a development of 35 horse-power per ton of coal burned in twelve hours. (3) When a furnace is supplied with, a boiler capable of absorbing one-half of all the heat created at the highest temperature of the furnace, the average loss throughout the day will be one-third of the total made, or one-half of what is utilized, this being due to the fact that this limited capacity is enough at certain periods, and that the boiler makes beyond its rated and economical capacity, as shown by the great loss of heat in the escaping gases. (4) When a furnace is equipped with ample boiler capacity, the horse-power developed by each ton of coal put into the firebox will be one-half as much as would be developed by the same coal if burned under an ordinary stationary boiler. In Table IX-E are given analyses of the waste gases from soft-coal reverberatory furnaces after passing through boilers. In the first column is given the interval from the time when the furnace was charged to the time when the test was taken, and in the second column is given the number of tests that were averaged to give the composition stated. Observations were made as to the time when fresh coal was added, but the analyses did not seem to show any relation thereto. Thus there were 14 tests showing over 6 per cent. CO, and the average time since coaling for these was 13 minutes. There were 20 tests showing less than 3 .per cent. 00, and the average time since coaling was 16 minutes. There were 8 tests with over 6 per cent, oxygen, and the average time since coaling was 16 minutes.